Semiconductor integrated circuit device in which a conductive film is formed over a trap film which in turn is formed over a titanium film

ABSTRACT

The semiconductor device is formed according to the following steps. A TiN film 71 and a W film 72 are deposited on a silicon oxide film 64 including the inside of a via-hole 66 by the CVD method and thereafter, the W film 72 and TiN film 71 on the silicon oxide film 64 are etched back to leave only the inside of the via-hole 66 and form a plug 73. Then, a TiN film 74, Al-alloy film 75, and Ti film 76 are deposited on the silicon oxide film 64 including the surface of the plug 73 by the sputtering method and thereafter, the Ti film 76, Al-alloy film 75, and TiN film 74 are patterned to form second-layer wirings 77 and 78.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor integrated circuitdevice and a technique of fabricating a semiconductor integrated circuitdevice, and more particularly to measures for preventing corrosion of anupper-layer wiring when a TiN film is formed inside a through-hole forconnecting upper- and lower-layer wiring formed over a semiconductorsubstrate and over an upper electrode of a capacitor insulating film, bya chemical vapor deposition method using a metal source containing ahalogen element.

When the aspect ratio of a through-hole (depth/diameter of thethrough-hole) for connecting upper- and lower-layer wirings formed on asemiconductor substrate is increased as an LSI is further refined andmore densely integrated, it is difficult to deposit a conductive filmfor wiring in the through-hole. Therefore, an art for embedding a plugin a through-hole having a high aspect ratio in a plug has been used sofar.

As described in Japanese Patent Laid-Open No. 204144/1996, to preventreaction between a metal wiring layer in a microminiaturized contacthole and an underlying layer, a titanium nitride (TiN) film is used as areaction barrier layer.

The titanium nitride film, when deposited by a CVD (Chemical VaporDeposition) method, has a good coverage and is thus widely used as aplug material buried in a through-hole with a high aspect ratio. Forexample, Japanese Patent Laid-Open No. 45770/1997 discloses a techniquewhereby a TiN film is formed by a CVD method inside a through-holeformed in an interlayer insulating film and a tungsten film or atungsten compound is formed over the TiN film.

A technique has been developed which deposits a TiN film as an upperelectrode by a CVD method over a tantalum oxide film which is acapacitive insulating film of a capacitor. For example, Japanese PatentLaid-Open No. 219501/1997 discloses a technique for forming a TiN filmas an upper electrode over a tantalum oxide film as a capacitorinsulating film by a CVD method.

To deposit a TiN film by the CVD method, a source gas containing ahalogen element such as titanium tetrachloride (TiCl₄) is generallyused. This is because a TiN film formed by using the source gas has alarge step coverage and moreover, the film can be formed at a lowtemperature of approx. 450° C. and thereby, there is an advantage thatthe characteristic of a device is not deteriorated.

However, because a TiN film formed by using a source gas containing ahalogen element contains a halogen element such as chlorine produced dueto decomposition of the source gas, there is a problem that the Al(aluminum) wiring formed on a through-hole in which a CVD-TiN film isembedded would be corroded because the halogen element reacts with Al.In a method of forming a tungsten film or tungsten compound film over atitanium nitride film buried in a through-hole, as described in JapanesePatent Laid-Open No. 45770/1997, although the tungsten film has agreater capability to trap halogen elements than a tungsten compoundfilm such as a tungsten nitride film, the overall effect of trappinghalogen elements by the tungsten film is small, allowing halogenelements to enter the aluminum wiring layer formed over the tungstenfilm, and resulting in the halogen elements corroding the aluminum.Further, the tungsten film has a poor adhesion to the underlying filmand is easily peeled.

An object of the present invention is to provide a method of preventingcorrosion of an Al wiring formed over a through-hole in which a CVD-TiNfilm is buried or a technique of preventing corrosion of an Al wiringformed over the CVD-TiN film as an upper electrode of a capacitorinsulating film.

SUMMARY OF THE INVENTION

The outline of the present invention is briefly described below.

Between the titanium nitride film formed by using a gas containinghalogen as a source gas and a second conductive film is provided a filmwhich contains metal atoms that tend to bond to halogen elements andwhich has a higher capability to trap halogen elements than tungsten.The provision between the titanium nitride film and the secondconductive film of a film that traps halogen elements--which corrode thesecond conductive film such as an aluminum film--can prevent thediffusion of the halogen elements into the second conductive film andtherefore the corrosion of the second conductive film.

The trap film that contains metal atoms tending to bond to halogenelements and has a higher capability to trap halogen than tungsten maybe a titanium film, a titanium nitride film, a tantalum film or atantalum nitride film, all these formed by the sputtering method, and atitanium film, a titanium nitride film, a tantalum film or a tantalumnitride film, all these formed by the CVD method using a source gas notcontaining halogen as constitutional elements. Any of these films may beused as a single layer and also as a multilayer film two or more layersof these films. When used as a single layer, the titanium film formed bythe sputtering method has the greatest capability to trap halogenelements. When a multilayer film comprising a titanium film formed bysputtering and a titanium nitride film formed by sputtering is used,because the titanium film has a higher trapping capability, a greatercorrosion prevention effect can be produced if the titanium film is madethicker than the titanium nitride film. These trap films are preferablyformed to a thickness of more than 5 nm, more preferably 20 nm or more,either as a single layer film or as a multilayer film. A thickness inexcess of 120 nm results in increased resistance and is practically notpreferable. The provision of such a trapping layer improves the adhesionbetween the titanium nitride film containing a halogen element and theinterlayer insulating film.

The trap film is a film containing atoms with a halogen bonding energyin excess of 111 kcal/mol. The greater the bonding energy, the greaterthe capability to trap halogen. In practice it is necessary for thebonding energy to be 111 kcal/mol or higher.

The effect to prevent corrosion of this trap film when the trap film isprovided immediately below the second conductive film is equivalent tothe effect when one or more additional layers are provided between thesecond conductive film and the trap film.

The trap film such as a titanium film exhibits an excellent capabilityto trap halogen even when a gas containing, fluorine, bromine or iodine,not to mention chlorine, as a constitutional element is used for asource gas for the titanium nitride film. Among examples of the sourcegas containing halogen are titanium tetrachloride and titaniumtetraiodide. Titanium tetrachloride exhibits the highest corrosivenessfor metals, particularly when it is used as a source gas, and there is adefinite reason to provide a trap film.

The second conductive film is a film that may be corroded and which ismade of aluminum, aluminum alloy, copper or copper alloy.

The trap film is formed over the opening after the titanium nitride filmcontaining a halogen element has been formed by the CVD method in theopening of the insulating film. In more detail, the first conductivefilm including a titanium nitride film formed by the CVD method using asource gas containing halogen is deposited over the insulating film onthe substrate through the opening in the insulating film. After this,the first conductive film over this insulating film is removed to form aplug inside the opening and a second conductive film including as alowermost layer a second titanium nitride film formed by the sputteringmethod is deposited over the insulating film including the plug surface.This second conductive film is patterned to form a wiring layer. Thefirst conductive layer may be a multilayer film of a titanium nitridefilm and a tungsten film formed by the CVD method or a single layer filmof a titanium nitride film formed by the CVD method. Alternatively, thefirst conductive film including a titanium nitride film formed by theCVD method using a source gas containing halogen as a constitutionalelement is deposited over the insulating film through the opening in theinsulating film on the substrate where a MISFET and a capacitor isformed. After this, the first conductive film over this insulating filmis removed to form a plug inside the opening and a second conductivefilm including as a lowermost layer a second titanium nitride filmformed by the sputtering method is deposited over the insulating filmincluding the plug surface. This second conductive film is patterned toform a wiring layer. In this case, too, the first conductive layer maybe a multilayer film of a titanium nitride film and a tungsten filmformed by the CVD method or a single layer of a titanium nitride filmformed by the CVD method.

In the semiconductor device using a copper wiring layer, which iscorroded particularly easily, the copper corrosion can be mitigated byproviding a trap film such as of tantalum or tantalum nitride betweenthe titanium nitride film containing a halogen element and the copperwiring layer.

When the titanium nitride film formed by the CVD method is used for oneof the electrodes of the capacitor, the trap film such as a titaniumfilm made by sputtering is formed over this titanium nitride film.Conventionally, polysilicon has primarily been used for the electrodesof capacitors. Polysilicon films must be formed at a high temperature ofabout 650° C. The film making temperature can be reduced by the use atitanium nitride film formed by a CVD method using a source gascontaining halogen as a constitutional element. The film makingtemperature of the titanium nitride film by the CVD method is 400° C. to600° C. The relation between chlorine concentration in the titaniumnitride film and the film making temperature when titanium tetrachlorideis used as a source gas is shown in FIG. 46. As shown in this graph,lower film making temperature results in higher chlorine concentrationin the titanium nitride film. Particularly when the film is made attemperatures below 500° C., the extent to which the wiring layer aroundthe storing capacitor is corroded increases. Thus, the effect to preventcorrosion of the wiring layer becomes great if the trap film of thisinvention is provided particularly when the titanium nitride film isformed at temperatures below 500° C. Not only when a titanium nitridefilm containing halogen is formed as the storage electrode but also whena titanium nitride film is formed after an aluminum wiring layer hasbeen formed, it is preferable that the film making temperature be below500° C. Forming the film at low temperatures increases the content ofhalogen in the titanium nitride film.

The corrosion of the conductive film can also be prevented by forming atitanium nitride film using a source gas containing halogen as aconstitutional element and then annealing it in an inert gas such asnitrogen gas or rare gas. That is, annealing can remove halogen from thetitanium nitride film. The annealing is performed at a temperature of400° C. to 800° C., preferably at a temperature higher than that of theprocess in which a TiN film is formed by the CVD method. If annealing isdone in the same apparatus as the film making apparatus without exposingthe titanium nitride film to the atmosphere immediately after thetitanium nitride film is formed, the oxidation of the surface of thetitanium nitride film can be prevented. The cleaning process may beomitted. If the cleaning process is performed, it may be done eitherbefore or after the annealing, preferably after annealing. The use ofwarm water at 40° C. or higher during cleaning is most effective inremoving chlorine.

If water enters the titanium nitride film during a certain processing,chlorine becomes more freely movable in the device and thus the amountof chlorine moving toward the wiring layer increases, rendering thewiring layer more likely to be corroded. It is considered that thereason is because chlorine in the titanium nitride film, when contactingwater, is ionized and become more freely movable seeking species to bondto. To prevent ingress of water into the titanium nitride film, thetitanium nitride film is formed by using a source gas containing halogenas a constitutional element, followed by the forming of a high-densityplasma CVD insulating film that has a high water blocking effect. Therefractive index of the insulating film is above 1.46, and theinsulating film includes Si rich. The processes during which water canenter the film include the cleaning process after dry etching and theinorganic spin-on-glass (SOG) film forming process. The inorganic SOGfilm forming process involves applying an inorganic SOG film and thenperforming a steam-baking whereby the film is baked in water steam.Thus, by forming a high-density plasma CVD insulating film under theinorganic SOG film, the corrosion of the wiring layer can be reduced. Anorganic SOG film may be formed instead of the high-density plasma CVDfilm because the organic SOG film also has a water blocking capability,though not as high as that of the high-density plasma CVD insulatingfilm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall top view of a semiconductor chip on which the DRAMof an embodiment of the present invention is formed;

FIG. 2 is an equivalent circuit diagram of the DRAM of an embodiment ofthe present invention;

FIG. 3 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 4 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 5 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 6 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 7 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 8 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 9 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 10 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 11 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 12 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 13 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 14 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 15 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 16 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 17 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 18 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 19 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 20 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 21 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 22 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 23 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 24 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 25 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 26 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 27 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 28 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 29 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 30 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 31 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 32 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 33 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 34 is a top view of an essential portion of a semiconductorsubstrate showing the pattern of a groove and the pattern of a longgroove;

FIG. 35 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 36 is a sectional view of an essential portion of a semiconductorsubstrate showing a fabrication method of the DRAM of an embodiment ofthe present invention;

FIG. 37 is a sectional view of an essential portion of a semiconductorshowing a fabrication method of the DRAM of an embodiment of the presentinvention;

FIG. 38 is a sectional view of an essential portion of a semiconductorshowing a fabrication method of the DRAM of an embodiment of the presentinvention;

FIG. 39 is a sectional view of an essential portion of a semiconductorshowing a fabrication method of the DRAM of an embodiment of the presentinvention;

FIG. 40 is a sectional view of an essential portion of a semiconductorshowing a fabrication method of the DRAM of an embodiment of the presentinvention;

FIG. 41 is a sectional view of an essential portion of a semiconductorshowing a fabrication method of the DRAM of an embodiment of the presentinvention;

FIG. 42 is a sectional view of an essential portion of a semiconductorshowing a fabrication method of the DRAM of an embodiment of the presentinvention;

FIG. 43 is a sectional view of an essential portion of a semiconductorshowing a fabrication method of the DRAM of an embodiment of the presentinvention;

FIG. 44 is a sectional view of an essential portion of a semiconductorshowing a fabrication method of the DRAM of an embodiment of the presentinvention;

FIG. 45 is a sectional view of an essential portion of a semiconductorshowing a fabrication method of the DRAM of an embodiment of the presentinvention;

FIG. 46 is a diagram showing the relation between the film formingtemperature of the titanium nitride film by the CVD method and thechlorine density of the titanium nitride film;

FIG. 47 is a cross section of a storing capacitor section of a DRAMaccording to this invention;

FIG. 48 is a cross section of a storing capacitor section of a DRAMaccording to this invention;

FIG. 49 is a cross section of a storing capacitor section of a DRAMaccording to this invention;

FIG. 50 is a diagram showing the flow of the process for removingchlorine from the titanium nitride film according to this invention;

FIG. 51 is a cross section of a storing capacitor section of a DRAMaccording to this invention;

FIG. 52 is a cross section of a storing capacitor section of a DRAMaccording to this invention;

FIG. 53 is a cross section of a storing capacitor section of a DRAMaccording to this invention;

FIG. 54 is a cross section of a storing capacitor section of a DRAMaccording to this invention;

FIG. 55 is a cross section of a storing capacitor section of a DRAMaccording to this invention; and

FIG. 56 is a cross section of a storing capacitor section of a DRAMaccording to this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

The preferred embodiments of the present invention are described belowin detail by referring to the accompanying drawings. Similar elementsare provided with the same symbol and their repetitive description isomitted.

FIG. 1 is a top view of a semiconductor chip on which the DRAM of thisembodiment is formed. As shown in FIG. 1, a lot of memory arrays MARYare arranged on the principal plane of a semiconductor chip 1A made ofsingle-crystal silicon like a matrix along the X direction (major-sidedirection of the semiconductor chip 1A) and the Y direction (minor-sidedirection of the semiconductor chip 1A). A sense amplifier SA is setbetween the memory arrays MARY adjacent to each other along X direction.Control circuits such as a word driver WD and a data-line selectioncircuit and an input/output circuit and a bonding pad are arranged atthe central portion of the principal plane of the semiconductor chip 1A.

FIG. 2 is an equivalent circuit diagram of the DRAM. As shown in FIG. 2,the memory array (MARY) of the DRAM comprises a plurality of word linesWL (WLn-1, WLn, WLn+1, . . . ) arranged like a matrix, a plurality ofbit lines BL, and a plurality of memory cells arranged at theintersections of the word lines WL and bit lines BL. One memory cell forstoring the information for 1 bit comprises one information storingcapacitive element C and one memory cell selecting MISFET Qsseries-connected with the element. One source and drain of the memorycell selecting MISFETs are electrically connected with the informationstoring capacitive element C and the other source and drain areelectrically connected with the bit lines BL. One end of the word lineWL is connected to the word driver WD and one ends of the bit lines BLare connected to the sense amplifier SA.

Then, the method of this embodiment for fabricating a DRAM is describedbelow in order of step by referring to FIGS. 3 to 45.

First, as shown in FIG. 3, a p-type semiconductor substrate 1 having aresistivity of approx. 10 Ωcm is wet-oxidized at approx. 85° C. to forma thin silicon oxide film 2 having a thickness of approx. 10 nm on thesurface of the substrate 1 and thereafter, deposit a silicon nitridefilm 3 having a thickness of approx. 140 nm on the silicon oxide film 2by the CVD (Chemical Vapor Deposition) method. The silicon oxide film 2is formed to moderate the stress added to a substrate when sintering asilicon oxide film to be embedded into the inside of a device separationgroove in the subsequent process. Because the silicon nitride film 3 hasa characteristic that it is hardly oxidized, it is used as a mask forpreventing the oxidization of the substrate surface below the film 3(active region).

Then, as shown in FIG. 4, a groove 5a having a depth of 300 to 400 nm isformed on the semiconductor substrate 1 in a device separation region byusing a photoresist film 4 as a mask and thereby, dry-etching thesilicon nitride film 3, silicon oxide film 2, and semiconductorsubstrate 1. To form the groove 5a, it is also possible to dry-etch thesilicon nitride film 3 by using the photoresist film 4 as a mask andthen remove the photoresist film 4 and thereafter, dry-etch the siliconoxide film 2 and semiconductor substrate 1 by using the silicon nitridefilm 3 as a mask.

Then, after removing the photoresist film 4, as shown in FIG. 5 thesemiconductor substrate 1 is wet-oxidized at 850 to 900° C. to remove adamage layer produced on the inner wall of the groove 5a due to theabove etching and form a thin silicon oxide film 6 having a thickness ofapprox. 10 nm on the inner wall of the groove 5a.

Then, as shown in FIG. 6, a silicon oxide film 7 having a thickness of300 to 400 nm is deposited on the semiconductor substrate 1a andthereafter, the semiconductor substrate 1 is dry-oxidized at approx.1000° C. to perform sintering for improving the quality of the siliconoxide film 7 embedded in the groove 5a. The silicon oxide film 7 isdeposited by the thermal CVD method using ozone (O₃) andtetraethoxysilane (TEOS) as source gases.

Then, a silicon nitride film 8 having a thickness of approx. 140 nm isdeposited on the silicon oxide film 7 by the CVD method as shown in FIG.7 and thereafter, dry-etched by using a photoresist film 9 as a mask asshown in FIG. 8 to leave the silicon nitride film 8 only on the groove5a having a relatively large area like the boundary between a memoryarray and a peripheral circuit region. The silicon nitride film 8 lefton the groove 5a is formed to prevent the phenomenon (dishing) in whichthe silicon oxide film 7 inside of the groove 5a having a relativelylarge area from being deeply polished compared to the silicon oxide film7 inside of the groove 5a having a relatively small area when flatteningthe silicon oxide film 7 by polishing it by the CMP method in the nextstep.

Then, the photoresist film 9 is removed and thereafter, a deviceseparation groove 5 is formed by polishing the silicon oxide film 7 bythe CMP method using the silicon nitride films 3 and 8 as stoppers andleaving the film 7 in the groove 5a.

Then, the silicon nitride films 3 and 8 are removed by the wet etchingusing hot phosphoric acid and thereafter, ions of an n-type impuritysuch as P (phosphorus) are implanted into the semiconductor substrate 1in the region (memory array) where a memory cell is formed to form ann-type semiconductor region 10 as shown in FIG. 10, ions of p-typeimpurity such as B (boron) is implanted into the memory array and a partof the peripheral circuit region (region where an n-channel MISFET isformed) to form a p-type well 11, and ions of an n-type impurity such asP (phosphorus) are implanted into other part of the peripheral circuitregion (region where a p-channel MISFET is formed) to form an n-typewell 12. Moreover, after the ion implantation, an impurity for adjustingthe threshold voltage of the MISFET such as BF₂ (boron fluoride) areimplanted into the p-type well 11 and n-type well 12. The n-typesemiconductor region 10 is formed to prevent noises from entering thep-type well 11 of the memory array from an input/output circuit or thelike through the semiconductor substrate 1.

Then, the silicon oxide film 2 of the surfaces of the p-type well 11 andn-type well 12 is removed by an HF(hydrofluoric acid)-based cleaningsolvent and thereafter, the semiconductor substrate 1 is wet-oxidized atapprox. 850° C. to form a clean gate oxide film 13 on the surfaces ofthe p-type well 11 and n-type well 12 respectively.

Though not restricted, by forming the gate oxide film 13 and thereafter,heat-treating the semiconductor substrate 1 in an NO (nitrogen oxide)environment or an N₂ O (nitrogen suboxide) environment, it is possibleto segregate nitrogen at the interface between the gate oxide film 13and the semiconductor substrate 1 (oxidation-nitration treatment). Whenthe thickness of the gate oxide film 13 decreases up to approx. 7 nm, astrain produced at the interface between the gate oxide film 13 and thesemiconductor substrate 1 is realized due to the difference betweentheir thermal expansion coefficients to cause hot carriers to occur.Because the nitrogen segregated at the interface with the semiconductorsubstrate 1 moderates the strain, the oxidation-nitration treatment canimprove the reliability of the thin gate oxide film 13.

Then, as shown in FIG. 11, gate electrodes 14A, 14B, and 14C are formedon the gate oxide film 13. The gate electrode 14A constitutes a part ofa memory cell selecting MISFET and is used as a word line WL in regionsother than an active region. The width or gate length of the gateelectrode 14A (word line WL) is set to a minimum value (e.g. approx.0.24 μm) in an allowable range capable of controlling the short channeleffect of the memory cell selecting MISFET and securing a thresholdvoltage. Moreover, the interval between adjacent gate electrodes 14A(word lines WL) is set to a minimum value (e.g. 0.22 μm) determined bythe resolution limit of photolithography. The gate electrodes 14B and14C constitute a part of the n-channel MISFET and p-channel MISFETserving as peripheral circuits.

The gate electrodes 14A (word line WL), 14B, and 14C are formed bydepositing a polysilicon film having a thickness of approx. 70 nm dopedwith an n-type impurity such as P (phosphorus) on the semiconductorsubstrate 1 by the CVD method, then depositing a WN (tungsten nitride)film having a thickness of approx. 50 nm and a W film having a thicknessof approx. 100 nm on the polysilicon film by the sputtering method. Thena silicon nitride film 15 having a thickness of approx. 150 nm isdeposited on the WN film and W film by the CVD method, and thereafterthese films are patterned by using a photoresist film 16 as a mask. TheWN film functions as a barrier layer for preventing a silicide layerfrom being formed at the interface between the W film and thepolysilicon film because the both films react on each other underhigh-temperature heat treatment. The barrier layer can use not only theWN film but also a TiN (titanium nitride) film.

When constituting a part of the gate electrode 14A with alow-resistivity metal (W), it is possible to decrease the sheetresistivity of the electrode 14A up to 2 to 2.5 Ω/□. Therefore, it ispossible to decrease the delay of a word line. Moreover, because a wordline delay can be decreased without lining a gate electrode 14 (wordline WL) with an Al wiring, it is possible to further decrease thenumber of wiring layers formed on a memory cell.

Then, the photoresist 16 is removed and thereafter, dry etching residueand photoresist residue left on the surface of the semiconductorsubstrate 1 are removed by using an etching solution such ashydrofluoric acid. When the wet etching is performed, the gate oxidefilm 13 in regions other than the lower sides of the gate electrode 14A(word line WL) and the gate electrodes 14B and 14C is chipped andmoreover, the gate oxide film 13 at the lower side of the gate side wallis etched in isotropic manner and undercut occurs. Therefore, under theabove condition, the withstand voltage of the gate oxide film 13decreases. Thus, the quality of the chipped gate oxide film 13 isimproved by wet-oxidizing the semiconductor substrate 1 at approx. 900°C.

Then, as shown in FIG. 12, ions of a p-type impurity such as B (boron)are implanted into the n-type well 12 to form a p-type semiconductorregion 17 on the n-type well 12 at the both sides of the gate electrode14C. Moreover, ions of an n-type impurity such as P (phosphorus) areimplanted into the p-type well 11 to form an n-type semiconductor region18 on the p-type well 11 at the both sides of the gate electrode 14B andform an n-type semiconductor region 19 on the p-type well 11 at the bothsides of the gate electrode 14A. Thereby, memory cell selecting MISFETQs is formed on the memory array.

Then, a silicon nitride film 20 having a thickness of 50 to 100 nm isdeposited on the semiconductor substrate 1 by the CVD method as shown inFIG. 13 and thereafter, as shown in FIG. 14 the silicon nitride film 20of the memory array is covered with a photoresist film 21, andanisotropic etching is applied to the silicon nitride film 20 in theperipheral circuit region to form a side wall spacer 20a on the sidewalls of the gate electrodes 14B and 14C. This etching is performed byusing an etching gas so that the etching rate of the silicon nitridefilm 20 becomes larger than that of a silicon oxide film in order tominimize the amount of the gate oxide film 13 to be chipped or thesilicon oxide film 7 embedded in the device separation groove 5.Moreover, to minimize the amount of the silicon nitride film 15 to bechipped on the gate electrodes 14B and 14C, the degree of over-etchingis minimized.

Then, the photoresist 21 is removed and thereafter, as shown in FIG. 15,ions of a p-type impurity such as B (boron) are implanted into then-type well 12 in the peripheral circuit region to from a p⁺ -typesemiconductor region 22 (source and drain) of the p-channel MISFET andions of a n-type impurity such as As (arsenic) are implanted into thep-type well 11 in the peripheral circuit region to form an n⁺ typesemiconductor region 23 (source and drain) of the n-channel MISFET.Thereby, a p-channel MISFET Qp and n-channel MISFET Qn respectivelyhaving an LDD (Lightly Doped Drain) groove in the peripheral circuitregion are formed.

Then, as shown in FIG. 16, a SOG (spin-on-glass) film 24 having athickness of approx. 300 nm is spin-coated on the semiconductorsubstrate 1 and thereafter, the semiconductor substrate 1 isheat-treated at 800° C. for approx. 1 min to sinter the SOG film 24.

Then, as shown in FIG. 17, a silicon oxide film 25 having a thickness ofapprox. 600 nm is deposited on the SOG film 24 and thereafter, polishedby the CMP method to flatten the surface of the film 25. The siliconoxide film 25 is deposited by the plasma CVD method using ozone (O₃) andtetraethoxysilane (TEOS) as source gases.

Thus, in the case of this embodiment, the SOG film 24 having a highflatness is applied onto the gate electrode 14A (word line) and the gateelectrodes 14B and 14C even immediately after film formation andmoreover, the silicon oxide film 25 deposited on the film 24 isflattened by the CMP method. Thereby, the gap filling characteristic ofa small gap between the gate electrodes 14A (word lines WL) is improvedand it is possible to flatten an insulating film on the gate electrode14A (word line WL) and the gate electrodes 14B and 14C.

Then, as shown in FIG. 18, a silicon oxide film 26 having a thickness ofapprox. 100 nm is deposited on the silicon oxide film 25. The siliconoxide film 26 is deposited to repair fine scratches on the surface ofthe silicon oxide film 25 produced when the film 25 is polished by theCMP method. The silicon oxide film 26 is deposited by the plasma CVDmethod using ozone (O₃) and tetraethoxysilane (TEOS) as source gases.Moreover, it is possible to deposit a PSG (Phospho Silicate Glass) filmon the silicon oxide film 25 instead of the silicon oxide film 26.

Then, as shown in FIG. 19, the silicon oxide films 26 and 25 and the SOGfilm 24 on the n-type semiconductor region (source and drain) of thememory cell selecting MISFET Qs are removed by the dry etching using aphotoresist film 27 as a mask. This etching is performed underconditions in which etching rates of the silicon oxide films 26 and 25and the SOG film 24 for the silicon nitride film 20 increase so that thesilicon nitride film 20 covering the upper sides of the n-typesemiconductor region 19 and the device separation groove 5 are notcompletely removed.

Then, as shown in FIG. 20, the silicon nitride film 15 and the gateoxide film 13 on the n-type semiconductor region 19 (source and drain)of the memory cell selecting MISFET Qs are removed by the dry etchingusing the photoresist film 27 as a mask to form a contact hole 28 on theupper side of one side of the n-type semiconductor 19 (source and drain)and a contact hole 29 on the upper side of the other side of thesemiconductor 19.

The above dry etching is performed under a condition in which theetching rate of the silicon nitride film 20 becomes larger than that ofsilicon oxide films (the gate oxide film 13 and the silicon oxide film 7in the device separation groove 5) so that the n-type semiconductorregion 19 or device separation groove 5 is not deeply chipped. Moreover,the etching is performed under a condition in which the silicon nitridefilm 20 is etched in anisotropic manner so that the silicon nitride film20 is left on the side wall of the gate electrode 14A (word line WL).Thereby, the contact holes 28 and 29 respectively having a fine diameterequal to or less than the resolution limit of photolithography areformed on the gate electrode 14A (word line WL) in self-alignment. Toform the contact holes 28 and 29 on the gate electrode 14A (word lineWL) in self-alignment, it is also possible to previouslyanisotropy-etching the silicon nitride film 20 and form a side wallspacer on the side wall of the gate electrode 14A (word line WL).

Then, the photoresist film 27 is removed to remove the dry etchingresidue and photoresist residue from the substrate surface exposed tothe bottoms of the contact holes 28 and 29. In this case, the SOG film24 exposed to the side walls of the contact holes 28 and 29 is alsoexposed to an etching solution. However, because the etching rate of theSOG film 24 by a hydrofluoric-acid-based etching solution is decreasedbecause of the above sintering at approx. 800° C., the side wall of thecontact hole 28 or 29 is not greatly undercut by this wet etching.Thereby, it is possible to securely prevent plugs to be embedded in thecontact holes 28 and 29 in the next step from shortcircuiting eachother.

Then, as shown in FIG. 21, a plug 30 is formed inside of the contactholes 28 and 29 respectively. The plug 30 is formed by depositing apolysilicon film obtained by doping the upper side of the silicon oxidefilm 26 with an n-type impurity (e.g., phosphorus) and thereafter,polishing the polysilicon film by the CMP method and leaving the film inthe contact holes 28 and 29.

Then, as shown in FIG. 22, a silicon oxide film 31 having a thickness ofapprox. 200 nm is deposited on the silicon oxide film 26 and thereafter,the semiconductor substrate 1 is heat-treated at approx. 800° C. Thesilicon oxide film 31 is deposited by the plasma CVD method using, forexample, ozone (O₃) and tetraethoxysilane (TEOS) as source gases.According to this heat treatment, the n-type impurity in the polysiliconfilm constituting the plug 30 diffuses into the n-type semiconductorregion 19 (source and drain) of the memory cell selecting MISFET Qs fromthe bottoms of the contact holes 28 and 29 and the resistivity of then-type semiconductor region 19 is decreased.

Then, as shown in FIG. 23, the silicon oxide film 31 on the contact hole28 is removed by the dry etching using the photoresist film 32 as a maskto expose the surface of the plug 30. Then, the photoresist film 32 isremoved and as shown in FIG. 24, the silicon oxide films 31, 26, and 25,SOG film 24, and gate oxide film 13 in the peripheral circuit region areremoved by the dry etching using the photoresist film 33 as a mask toform contact holes 34 and 35 on the n⁺ -type semiconductor region 23(source and drain) of the n-channel MISFET Qn and form contact holes 36and 37 on the p⁺ -type semiconductor region 22 (source and drain) of thep-channel MISFET Qp.

Then, the photoresist film 33 is removed and thereafter, as shown inFIG. 25, the bit line BL and first-layer wirings 38 and 39 of peripheralcircuits are formed on the silicon oxide film 31. To form the bit lineBL and first-layer wirings 38 and 39, a Ti film having a thickness ofapprox. 50 nm is first deposited on the silicon oxide film 31 by thesputtering method to heat-treat the semiconductor substrate 1 at approx.800° C. Then, a TiN film having a thickness of approx. 50 nm isdeposited on the Ti film by the sputtering method and moreover, a W filmhaving a thickness of approx. 150 nm and a silicon nitride film 40having a thickness of 200 nm are deposited on the TiN film andthereafter, these films are patterned by using the photoresist film 41as a mask.

By depositing the Ti film on the silicon oxide film 31 and thenheat-treating the semiconductor substrate 1 at approx. 800° C., the Tifilm reacts on the Si substrate and a low-resistivity TiSi₂ (titaniumsilicide) layer 42 is formed on the surface of the n+-type semiconductorregion 23 (source and drain) of the n-channel MISFET Qn and the surfaceof the p⁺ -type semiconductor region 22 (source and drain) of thep-channel MISFET Qp. In this case, though not illustrated, the TiSi₂(titanium silicide) layer 42 is also formed on the surface of the plug30 embedded in the contact hole 28 on the n-type semiconductor region 19of the memory cell selecting MISFET Qs. Thereby, it is possible todecrease the contact resistivity of the wirings (bit line BL andfirst-layer wirings 38 and 39) to be connected to the n⁺ -typesemiconductor region 23 and p⁺ -type semiconductor region 22. Moreover,by constituting a bit line BL with a W film/TiN film/Ti film, it ispossible to decrease the sheet resistivity of a bit line BL up to 2 Ω/□or less. Therefore, it is possible to improve the read speed and writespeed of information and moreover, form a bit line BL and thefirst-layer wirings 38 and 39 of peripheral circuits in one step at thesame time and thus, decrease the number of DRAM fabrication steps.Moreover, when constituting the first-layer wirings (38 and 39) ofperipheral circuits with wirings at the same layer as a bit line BL, theconnection reliability of the firs-layer wirings is improved compared tothe case of constituting the first-layer wirings with Al wiring of theupper layer of a memory cell because the aspect ratios of contact holes(34 to 37) for connecting MISFETs (n-channel MISFET Qn and p-channelMISFET Qp) of peripheral circuits with the first-layer wirings aredecreased.

Bit lines BL are formed so that the interval between them becomes longerthan the width of each bit line BL in order to improve the informationread speed and write speed by decreasing the parasitic capacitanceformed between adjacent bit lines BL. The interval between the bit linesBL is set to, for example, approx. 0.24 μm and the width of each bitline BL is set to, for example, approx. 0.22 μm.

Then, the photoresist 41 is removed and thereafter, as shown in FIG. 26,a side wall spacer 43 is formed between the side wall of a bit line BLand those of the first-layer wirings 38 and 39. The side wall spacer 43is formed by depositing a silicon nitride film on the bit line BL andfirst-layer wirings 38 and 39 by the CVD method and thereafteranisotropy-etching the silicon nitride film.

Then, as shown in FIG. 27, surfaces of a bit lines BL and thefirst-layer wirings 38 and 39 are spin-coated with an SOG film 44 havinga thickness of approx. 300 nm. Then, the semiconductor substrate 1 isheat-treated at 800° C. for approx. 1 min to sinter the SOG film 44.

Because the SOG film 44 has a reflowing characteristic higher than thatof a BPSG film and is superior in gap filling characteristic betweenfine wirings, it is possible to smoothly fill the gap between very finebit lines BL which are made fine up to about the resolution limit ofphotolithography. Moreover, the SOG film 44 has a high reflowingcharacteristic without performing high-temperature and long-time heattreatment required for a BPSG film, the film 44 makes it possible tocontrol thermal diffusion of impurities contained in the source anddrain of the memory cell selecting MISFET Qs formed on the lower layerof a bit line BL and the sources and drains of MISFETs (n-channel MISFETQn and p-channel MISFET Qp) of peripheral circuits and realize shallowconjunction. Furthermore, because the film 44 makes it possible tocontrol the deterioration of metals (W films) constituting the gateelectrode 14A (word line) and the gate electrodes 14B and 14C, it ispossible to improve the performances of memory cells of a DRAM andMISFETs constituting peripheral circuits. Furthermore, the film 44 makesit possible to control the deterioration of a Ti film, TiN film, and Wfilm constituting a bit line BL and the first-layer wirings 38 and 39and decrease the wiring resistivity.

Then, as shown in FIG. 28, a silicon oxide film 45 having a thickness of600 nm is deposited on the SOG film 44 and thereafter, polished by theCMP method to flatten the surface of the film 45. The silicon oxide film45 is deposited by the plasma CVD method using, for example, ozone (O₃)and tetraethoxysilane (TEOS) as source gases.

Thus, in the case of this embodiment, the SOG film 44 having a highflatness is applied onto bit lines BL and the first-layer wirings 38 and39 even immediately after film formation and moreover, the silicon oxidefilm 45 deposited on the film 44 is flattened by the CMP method.Thereby, the filling characteristic of a fine gap between bit lines BLis improved and it is possible to flatten the insulating film on bitlines BL and the first-layer wirings 38 and 39. Moreover, becausehigh-temperature long-time heat treatment is not performed, it ispossible to prevent the deterioration of characteristics of memory cellsand MISFETs constituting peripheral circuits from deteriorating andrealize high performances and decrease resistivities of bit lines BL andthe first-layer wirings 38 and 39.

Then, as shown in FIG. 29, a silicon oxide film 46 having a thickness ofapprox. 100 nm is deposited on the silicon oxide film 45. The siliconoxide film 46 is deposited to repair fine scratches on the surface ofthe silicon oxide film 45 produced when polished by the CMP method. Thesilicon oxide film 46 is deposited by the plasma CVD method using, forexample, ozone (O₃) and tetraethoxysilane (TEOS) as source gases.

Then, as shown in FIG. 30, the silicon oxide films 46 and 45, SOG film44, and silicon oxide film 31 on the contact hole 29 are removed by thedry etching using the photoresist film 47 as a mask to form a via-holereaching the surface of the plug 30. This etching is performed under acondition in which the etching rate of a silicon nitride film becomessmaller than those of the silicon oxide films 46, 45, and 31 and SOGfilm 44 so that the silicon nitride film 40 on a bit line BL and theside wall spacer 43 are not deeply chipped even if misalignment betweenthe via-hole 48 and a bit line BL occurs. Thereby, the via-hole 48 isformed on the bit line BL in self-alignment.

Then, the photoresist film 47 is removed and thereafter, the dry etchingresidue and photoresist residue are removed from the surface of the plug30 exposed to the bottom of the via-hole 48 by using an etching solutionsuch as a mixed solution of hydrofluoric acid and ammonium fluoride. Inthis case, the SOG film 44 exposed to the side wall of the via-hole 48is also exposed to the etching solution. However, because the etchingrate of the SOG film 44 by a hydrofluoric-acid-based etching solution isdecreased due to the sintering at approx. 800° C., the side wall of thevia-hole 48 is not greatly undercut by the wet etching. Thereby, it ispossible to securely prevent the plug embedded in the via-hole 48 fromshort-circuiting with a bit line BL in the next step. Moreover, becausethe plug can be adequately separated from the bit line BL, it ispossible to control the increase of the parasitic capacitance of the bitline BL.

Then, as shown in FIG. 31, a plug 49 is formed inside of the via-hole48. The plug 49 is formed by depositing a polysilicon film doped with ann-type impurity (e.g., phosphorus) on the silicon oxide film 46 by theCVD method and thereafter, etching back the polysilicon film to leave itin the via-hole 48.

Then, as shown in FIG. 32, a silicon nitride film 51 having a thicknessof approx. 100 nm is deposited on the silicon oxide film 46 by the CVDmethod to remove the silicon nitride film 51 in the peripheral circuitregion by the dry etching using the photoresist film 52 as a mask. Thesilicon nitride film 51 left in the memory array is used as an etchingstopper when etching the silicon oxide film between bottom electrodes inthe step of forming a bottom electrode of an information storingcapacitive element to be described later.

Then, the photoresist film 52 is removed and thereafter, as shown inFIG. 33, a silicon oxide film 53 having a thickness of approx. 1.3 μm isdeposited on the silicon nitride film 51 by the plasma CVD method using,for example, ozone (O₃) and tetraethoxysilane (TEOS) as source gases andthe silicon oxide film 53 and silicon nitride film 51 are removed by thedry etching using the photoresist film 51 as a mask to form a groove 55on the via-hole 48 in which the plug 49 is embedded. In this case, along belt-like groove 59 for enclosing a memory array is formed aroundthe memory array at the same time. FIG. 34 is a top view of an essentialportion of the semiconductor substrate 1 showing the pattern of thegroove 55 and that of the long groove 59.

Then, the photoresist 54 is removed and thereafter, as shown in FIG. 35,a polysilicon film 56 doped with an n-type impurity {e.g. P(phosphorus)} and having a thickness of approx. 60 nm is deposited onthe silicon oxide film 53. The polysilicon film 56 is used as thebottom-electrode material of an information storing capacitive element.

Then, as shown in FIG. 36, an SOG film 57 having a thickness enough toembed the groove 55 and long groove 59 (e.g. 300 to 400 nm) is depositedon the polysilicon film 56 and then, the SOG film 57 is baked via heattreatment at approx. 400° C. and thereafter, the SOG film 57 is etchedback to expose the polysilicon film 56 on the silicon oxide film 53 asshown in FIG. 37 and then, the film 56 is etched back to leave thepolysilicon film 56 in the insides (inner wall and bottom) of the groove55 and long groove 59. In this case, the SOG film 57 not etched back isalso left in the insides of the groove 55 and long groove 59.

Then, as shown in FIG. 38, the silicon oxide film 53 in the peripheralcircuit region is covered with a photoresist film 58 and the SOG film 57inside of the groove 55 and the silicon oxide film 53 in the gap of thegroove 55 are wet-etched by a hydrofluoric-acid-base etching solution toform a bottom electrode 60 of an information storing capacitive element.In this case, because the silicon nitride film 51 is formed at thebottom of the gap of the groove 55, the silicon oxide film 46 at thebottom of the gap is not chipped by an etching solution even if thesilicon oxide film 53 in the gap is completely removed.

One end of the photoresist film 58 covering the silicon oxide film 53 inthe peripheral circuit region is set on the boundary between the memoryarray and the peripheral circuit region, that is, on the long groove 59.Therefore, by performing the above wet etching, the SOG film 57 in thelong groove 59 is also removed. However, because the bottom electrodematerial (polysilicon film 56) on the inner wall of the long groove 59serves as an etching stopper, the side wall of the SOG film 57 is notchipped. Moreover, because the surface of the silicon oxide film 53 inthe peripheral circuit region is covered with the photoresist film 58,the surface is not chipped. Thereby, the step between the memory arrayand the peripheral circuit region is eliminated and moreover, theperipheral circuit region is flattened.

Then, the photoresist film 58 covering the peripheral circuit region isremoved, the semiconductor substrate 1 is heat-treated in ammoniaenvironment at approx. 800° C. in order to prevent the polysilicon film(56) constituting the bottom electrode 60 from oxidizing to nitrate thesurface of the polysilicon film (56) and thereafter, as shown in FIG.39, a Ta₂ O₅ (tantalum oxide) film 61 having a thickness of approx. 20nm is deposited on the bottom electrode 60 by the CVD method, and thesemiconductor substrate 1 is heat-treated at approx. 800° C. to repairdefects of the Ta₂ O₅ film 61. The Ta₂ O₅ film 61 is used as thecapacitance insulating film material of an information storingcapacitive element.

Next, as shown in FIG. 40, a TiN film is formed over the Ta₂ O₅ film 61to a thickness of 50-100 nm by the CVD method. The CVD-TiN film isdeposited by a thermal CVD method at a temperature of 400-650° C.,preferably 400-500° C., at a pressure of about 5-3000 Pa using a gasmixture (TiCl₄ /NH₃ =1/2 to 1/50) of titanium tetrachloride (TiCl₄) andammonia (NH₃) as a source gas. This CVD-TiN film forming conditionbrings about a good step coverage and a good dielectric strength of thecapacitor insulating film. The film, however, contains about 5% ofchlorine atoms or chlorine ions.

After the CVD-TiN film has been formed, another TiN film is sputtered toa thickness of 50-100 nm. The multilayer structure of thesputtered-TiN/CVD-TiN film enables the approximately 5% of chlorine orchlorine ions contained in the CVD-TiN film to be trapped by theoverlying spattered-TiN film, thus preventing the corrosion of the Alwiring formed in a later process due to chlorine present in the CVD-TiN.

After a TiN film 62 is deposited, the TiN film 62 and Ta₂ O₅ film 61 arepatterned by the dry etching using the photoresist film 63 as a mask toform an information storing capacitive element C comprising a topelectrode made of the TiN film 62, a capacitance insulating film made ofthe Ta₂ O₅, and the bottom electrode 60 made of the polysilicon film 56.Thereby, a DRAM memory cell comprising the memory cell selecting MISFETQs and the information storing capacitive element C connected to theMISFET Qs in series is almost completed.

Then, the photoresist film 63 is removed and thereafter, as shown inFIG. 41, a silicon oxide film 64 having a thickness of approx. 100 nm isdeposited on the information storing capacitive element C by the plasmaCVD method using, for example, ozone (O₃) and tetraethoxysilane (TEOS)as source gases, and the silicon oxide film 64, silicon oxide film 53,silicon oxide films 46 and 45, SOG film 44, and silicon nitride film 40are removed from the peripheral circuit region by the dry etching usingthe photoresist 65 as a mask to form a via-hole 66 having a large aspectratio on the first-layer wiring 38.

Then, the photoresist film 65 is removed and thereafter, as shown inFIG. 42, a TiN film 71 having a thickness of 5 to 50 nm, preferablyapprox. 50 nm is deposited on the silicon oxide film 64 including theinside of the via-hole 66. The TiN film 71 is deposited by the thermalCVD method at a temperature of 400 to 650° C., preferably 600° C. and apressure of 5 to 3000 Pa by using a mixed gas (TiCl₄ /NH₃ =1/2-1/50) oftitanium tetrachloride (TiCl₄) and ammonia (NH₃) as a source gas.Because the TiN film 71 has a large step coverage, the film thicknessbecomes almost uniform at the bottom and the opening of the via-hole 66.Moreover, the TiN film 71 contains approx. 5% of chlorine becausetitanium tetrachloride is used as the source gas.

Then, as shown in FIG. 43, a W film 72 having a thickness of approx. 500nm is deposited on the TiN film 71 by the CVD method and the W film 72and TiN film 71 on the silicon oxide film 64 are etched back and leftonly in the via-hole 66 to form a plug 73 made of a laminated film ofthe TiN film 71 and W film 72. To remove the W film 72 and TiN film 71from the surface of the silicon oxide film 64, it is also possible touse a chemical mechanical polishing (CMP) method.

Then, as shown in FIG. 44, a TiN film 74 having a thickness of approx.50 nm is deposited on the silicon oxide film 64 including the surface ofthe plug 73 by the sputtering method. Then, as shown in FIG. 45, anAl-alloy film 75 having a thickness of approx. 500 nm and a Ti film 76having a thickness of approx. 500 nm are deposited on the TiN film 74 bythe sputtering method and thereafter, the Ti film 76, Al-alloy film 75,and TiN film 74 are patterned by the dry etching using a photoresistfilm as a mask to form second-layer wirings 77 and 78 on the siliconoxide film 64.

Because the TiN film 71 (deposited by the CVD method) constituting apart of the plug 73 is separated from the Al-alloy film 75 constitutinga part of each of the second-layer wirings 77 and 78 by the TiN film 74deposited by the sputtering method, it is possible to prevent thesecond-layer wirings 77 and 78 from being corroded due to chlorinecontained in the TiN film 71 deposited by the CVE process.

The corrosion of the second-layer wirings 77, 78 due to chlorinecontained in the TiN film 71 deposited by the CVD method can beprevented also when a sputter Ti film, instead of the above sputter TiNfilm 74, is formed to a thickness of about 30 nm followed by theformation of another sputtered TiN film of about 30 nm. The sputtered Tifilm has a higher capability to trap chlorine than the sputtered TiNfilm.

While this embodiment uses the sputtered titanium nitride film 74, itmay also use a sputtered titanium film, tantalum film or tantalumnitride film.

The present invention can be applied to a process for forming a wiringout of a conductive film including an Al film over a via-hole in which aplug including a CVD-TiN film is buried.

Embodiment 2

This embodiment is an example where the device uses a titanium nitridefilm containing a halogen element as one of electrodes of a storingcapacitor section.

FIG. 47 shows a cross section of the capacitor. One electrode 101 of thecapacitor and a capacitor insulating film 102 of tantalum oxide areformed in the same manner as the embodiment 1. Although the capacitorinsulating film of this embodiment uses a tantalum oxide film, it mayuse a ferrodielectric film such as of BST and PZT. Then, using a gasmixture of titanium tetrachloride and ammonia as a source gas, atitanium nitride film 103 is formed to a thickness of 50-100 nm by thechemical vapor deposition method. This titanium nitride film is formedat about 500° C. and contains about 4% of chlorine. The upper electrodehas an advantage that when it is formed of titanium nitride instead ofconventionally used polysilicon, it can be formed at a lowertemperature. After this, a titanium film 104 is formed to a thickness ofabout 30 nm as a chlorine trap film over the chlorine containing TiNfilm 103.

In this way, although the titanium nitride film 103 contains a largeamount of chlorine, the formation of the titanium film 104 as a chlorinetrapping layer can effectively prevent corrosion of the wiring layeraround the capacitor.

Embodiment 3

This embodiment is an example in which a titanium nitride film 105 isformed by the sputtering method over the sputtered titanium film 104 ofthe Embodiment 2, and will be described referring to FIG. 48. Theprocess up to the formation of the capacitor insulating film of tantalumoxide is similar to those of Embodiment 1 and 2. After this, a titaniumfilm 104 was sputtered to a thickness of 40 nm and a titanium nitridefilm 105 formed to 60 nm by chemical conversion sputter using the flowof nitrogen gas. The use of a multilayer film of the titanium film 104formed by sputtering and the titanium nitride film 105 formed bysputtering as the chlorine trapping layer enabled almost completetrapping of chlorine and enhanced the effect to prevent corrosion of thewiring layer around the capacitor.

While, in this embodiment, the titanium film of 104 to 40 nm thicknessis formed by sputtering and the titanium nitride film of 105 to 60 nmthickness is formed, the thickness of the titanium film 104 may be 30-50nm and that of the titanium nitride film 105 to 50-100 nm.

Although, in this embodiment, a multilayer film of the titanium film 104and the titanium nitride film 105 is formed, a multilayer film of atantalum film 104 and a tantalum nitride film (TaN) 105 may be formed.In this case, too, the process involves forming a tantalum film and, ata certain stage of the process, flowing nitrogen gas while continuingthe forming of the tantalum film in order to form a tantalum nitridefilm. When the trap layer is a multilayer film as described above, thefilm deposition and the patterning such as etching can be facilitated ifthe multilayer film contains a common main constitutional element, likea multilayer film of titanium nitride film (upper layer)/a titanium film(lower layer) or a multilayer film of a tantalum nitride film (upperlayer)/a tantalum film (lower layer).

Embodiment 4

This embodiment is an example in which a titanium nitride filmcontaining a halogen element is used for one electrode of the storingcapacitor section and in which the upper and side portions of thetitanium nitride film are covered with the trap film. This example willbe described referring to FIG. 49.

As in Embodiment 2, a polysilicon film 101, a tantalum oxide film 102,and a halogen-containing titanium nitride film 103 are formed as astoring capacitor section. Then, a trap layer 106 is formed by aselective CVD method over the upper and side portions of the titaniumnitride film 103. The use of the selective CVD method ensures that thetrap film 106 can be formed not only over the halogen-containingtitanium nitride film 103 but over its side portions.

In addition to the above selective CVD method, a method shown in FIGS.55 and 56 may also be used to form the trap film 106 over the titaniumnitride film. First, a TiN film 106 as the trap layer is formed over thetitanium nitride film 103 of the upper electrode by the CVD method usinga source gas of TDMAT tetrakis(dimethylamino)titanium (FIG. 55). Next, aresist film 110 is formed over the upper and side surfaces of thetitanium nitride film 103 of the upper electrode (FIG. 56) and, usingthis resist as a mask, a TiN film 106 as a trap film is formed (FIG.49). Another organic source such as TDEAT tetrakis(diethylamino)titaniummay also be used.

By forming the trap film not only over the upper portion but over theside portions in such a way, it is possible to prevent the diffusion ofhalogen from the side portions of the titanium nitride film and therebyenhance the corrosion prevention effect on the wiring layer around thecapacitor.

Further, the trap layer may be a titanium film, a titanium nitride film,a tantalum film, or a tantalum nitride film formed by the sputteringmethod, or a titanium film, a titanium nitride film, a tantalum film, ora tantalum nitride film formed by the CVD method using a source gas notcontaining halogen as a constitutional element. The trap layer may alsobe a multilayer film of these.

Embodiment 5

This embodiment is a method of removing the halogen element from thehalogen-containing CVD-TiN film.

An example in which a titanium nitride film, formed by the CVD methodusing a source gas containing a halogen element as a constitutionalelement, is used as one of the electrodes of a storing capacitor sectionwill be described referring to the process flow diagram of FIG. 50.

First, a Ta₂ O₅ film, the capacitor insulating film, is formed and thena TiN film is formed over the Ta₂ O₅ film by the CVD method using asource gas of TiCl₄ and NH₃ at 450° C. This TiN film contains about 5%of chlorine.

Next, the device is heated at about 500° C. in a nitrogen atmosphere formore than 15 seconds, preferably about 10 minutes. This heat treatmentis carried out directly consecutively in the same apparatus withoutexposing the device to the open air. This heat treatment shouldpreferably be performed at an anneal temperature of 400-800° C.,preferably 500-650° C., which is higher than the film making temperatureof the CVD-TiN process because the higher annealing temperature resultsin a greater amount of chlorine removable from within, or from thesurface of, the TiN film. The heat treatment may be done by RTA (RapidThermal Anneal). Further, the heat treatment may be performed by usingthe same TiN film forming apparatus or a different apparatus. If thesame apparatus is used, the device can be annealed without being exposedto the atmosphere after the film is formed, enhancing the surfaceoxidation prevention effect. When the heat treatment is done using adifferent apparatus or chamber, on the other hand, the productivity(processing capability) improves.

The anneal can be performed in an inert gas atmosphere of Ar or He otherthan the above N₂. Other than such an inert gas, a reducing gas such asH₂ or NH₃ may be used. The use of a reducing gas requires care becausesuch a reducing gas, although it has a high capability to removechlorine from the CVD-TiN film, may deteriorate the dielectric strengthof the capacitor insulating film.

After this, chlorides such as NH₄ Cl deposited on the surface of thefilm are removed with pure water. The pure water cleaning is performedby applying the pure water to the rotating wafer, or by using pure waterto which ultrasonic vibration is applied, or by using a nylon brush asrequired. After cleaning, the wafer is dried on a hot plate heated to100-150° C. In addition to the pure water cleaning, the wafer may becleaned by a water solution containing 1-10% NH₃. Because the annealingprocess alone can remove chlorine of the film, the cleaning process isnot essential. But the cleaning process can remove chlorides adhering tothe surface of the film and therefore prevents corrosion effectively.

Then, after the photoresist and dry etch processes, the wafer undergoesthe pattern etch process for electrodes.

With these processes, chlorine in the TiN film can effectively beremoved and there is no need to provide any aforementioned trap layer.However, the combined use of the trap layer and the chlorine removingprocesses as in this embodiment can prevent the diffusion of chlorinealmost completely.

Embodiment 6

An embodiment is an example where an SiO film is formed over aninterlayer insulating film by the high-density plasma CVD method toprevent Al wiring corrosion will be described referring to FIGS. 51 and52 which show cross sections of a storing capacitor section.

In a similar manner to that of Embodiment 2, a polysilicon lowerelectrode 101 and a tantalum oxide capacitor insulating film 102 areformed. Then, a CVD-TiN film as the upper electrode of the capacitorinsulating film is formed to a thickness of about 100 nm by using TiCl₄.After the photoresist and dry etch processes, the upper electrode 104 ispatterned. Next, a TiN film 105 as the chlorine trap layer is formed toa thickness of 30 nm. This is followed by turning a gas mixture of SiH₄/O₂ /Ar introduced in the ECR plasma CVD apparatus to a plasma, applyinga high frequency wave of 13.56 MHz to a sample stage where a substrateis mounted, and drawing in Ar ions from the plasma to form an SiO₂ filmby the high-density plasma CVD method. In this way, an SiO₂ film 107having a water blocking capability is formed to about 400 nm (FIG. 51).The plasma CVD apparatus may be of a helical type or a helicon type inaddition to the ECR type. In this specification, the high density refersto a state of the plasma with ions in excess of 1×10¹⁰ (ions/cm³). It ishowever preferable to use a high-density plasma CVD method of a densityof 1×10¹² (ions/cm³).

Then, the SiO₂ film is partly removed by about 300 nm using CMP, leavingthe SiO₂ film 107 about 100 nm thick on the electrode. This filmcorresponds to the silicon oxide film 64 shown in FIG. 41.

Chlorine in the TiN film, when brought into contact with water that hasentered during some process, may corrode the surrounding wiring layereasily. Forming a high-density plasma insulating film, which has a highwater blocking effect, over the chlorine-containing titanium nitridefilm can prevent water from entering the titanium nitride film andtherefore prevent the corrosion of the surrounding wiring layer. Thiswater is produced on the upper layer of the chlorine containing TiN filmwhen the device is steam-baked after an inorganic spin-on-glass (SOG)film is applied or when it is cleaned after etching. Hence, theprovision of the high-density plasma SiO₂ film between the inorganic SOGfilm and the chlorine containing TiN film prevents entrance of waterinto the TiN film and produces a corrosion prevention effect. Thehigh-density plasma SiO₂ film needs to be provided between the inorganicSOG film and the halogen containing TiN film. This may be accomplishedeither by forming the inorganic SOG film 108 directly over thehigh-density plasma CVD insulating film 107 as in this embodiment (FIG.53) or by forming the wiring layer 109 over the high-density plasma CVDinsulating film 107 and then forming the inorganic SOG film 110 (FIG.54).

While this embodiment is an example where the TiN film is applied to theupper electrode of the capacitor, the use of the TiN film is not limitedto the capacitor. If the TiN film is applied to a part of the wiringlayer, a similar water blocking effect can be produced by forming ahigh-density plasma insulating film over the halogen containing TiNfilm.

While, in this embodiment, a high-density plasma CVD insulating film isprovided as a film having a high water blocking capability, an organicSOG film may also be used. It is noted, however, that the organic SOGfilm does not have as high a water block capability as the high-densityplasma CVD insulating film does.

Further, while the above embodiment is an example where halogen in thetitanium nitride film diffuses into the overlying wiring layer, theunderlying wiring layer can also be prevented from being corroded by atrap film formed under the titanium nitride film. For example, in astructure in which a tantalum or tantalum nitride film is formed as atrap film over a copper film which is highly corrodable, an insulatingfilm is formed, and further a halogen containing titanium nitride filmis formed thereover, the halogen from the overlying layer can be trappedby the tantalum or tantalum nitride film, which in turn preventscorrosion of the underlying copper film.

Further, while in the above embodiment the tantalum oxide is used as acapacitor insulating film, any of the materials including BaSrTiO₃,SrTiO₃, BaTiO₃, PZT, and ZnO doped with B (boron) or F (fluorine) canalso be applied. Such a material can also be used for a DRAM or anonvolatile memory.

The invention made by the present inventor is specifically describedabove in accordance with embodiments. However, the present invention isnot restricted to the embodiments. It is needless to say that variousmodifications of the present invention are allowed as long as they arenot deviated from the gist of the present invention.

ADVANTAGES OF THE PRESENT INVENTION

Advantages obtained from the present invention include those that arebriefly described below.

According to the present invention, it is possible to securely preventan Al wiring formed on a via-hole in which a plug including a CVD-TiNfilm is embedded from corroding. Therefore, it is possible to improvethe reliability and fabrication yield of LSIs having a via-hole of aparticularly high aspect ratio.

This invention can prevent corrosion of an Al wiring that is formed overthe capacitor element including the CVD-TiN film at the upper electrodeof the capacitor insulating film and therefore can improve thereliability of the Al wiring and the manufacturing yield withoutdegrading the dielectric strength of the capacitor insulating film.

What is claimed is:
 1. A semiconductor integrated circuit devicecomprising:a substrate where a MISFET is formed, a storing capacitivepart comprising a first electrode, a capacitor insulating film and asecond electrode including a titanium nitride film containing a halogenelement; a trap film formed over said titanium nitride film andcontaining an element having a bonding energy with the halogen elementin excess of 111 kcal/mol; and a conductive film formed over said trapfilm.
 2. A semiconductor integrated circuit device according to claim 1,wherein said trap film is formed to cover said titanium nitride film.